If the sketching-case is used on horseback, the operations are exactly the same as described above. To draw a direction, the horse is turned facing exactly in the direction of the object to be sighted, the case oriented, and the line drawn as before. A horse will generally stand still long enough for this. As the sketching approaches the far roller, the sketch is rolled up on the near roller and fresh paper brought upon the board.

Should the traverse, either because of a change in its general direction or because the meridian line was not given a proper direction, run off the side of the paper, sketching is stopped and a line drawn there across the paper. The case is turned in the new general direction of the traverse, as was done on commencing, the meridian line on the glass turned until over the needle, thus altering it to suit the new direction, and a new meridian line drawn on the fresh portion of paper parallel to the meridian line on the glass. The sketch is commenced in the center of the paper and 2 or 3 inches above the line drawn. If the running off is due to some local change of direction, and the general direction of the traverse still coincides with the central line of the paper, the meridian will usually remain unchanged.

Instead of making the alterations of meridian at the end of a course where there is a change of direction, it is better to proceed along the next course for a distance a little greater than the distance to which offsets are sketched in, and there make the change, thus avoiding the duplication of details in the smaller angles between the courses at the station, and the omission of others in the larger angle.

These alterations of the meridian may have to be made several times, but the necessity therefor should be avoided as much as possible by proper arrangement.

To finish the sketch. If it has been necessary to change. the meridian, the paper is cut across the lines where the changes were made, the corresponding points of stopping and recommencing the sketch are made to coincide by sticking a

pin through them into a board, the pieces are turned until their meridian lines are parallel, then firmly pinned in this position and both cut through with a sharp knife, passing through the coinciding points. The two pieces are then united by a strip of paper pasted on the back along the cut edges. When all are thus united, the traverse will follow along the middle of the irregularly shaped strip. This may then be mounted, if desired, on another piece of paper by its edges, and placed under a heavy weight while drying,

The Batson Sketching-Case differs from the one described in having on its upper surface a revolving and sliding graduated circular protractor carrying a small revolving alidade with

scales, all of which may be raised to an upright position; and on one end a pendulum clinometer, and in the other end holes for carrying pencils. The general principles of the use of this sketching-case are the same as those already described.

Sketching pad. For the field sketching-case, satisfactory results have been obtained by using a pad of suitable size, of good paper, backed with heavy cardboard, the paper being attached on all four edges. On the back of the pad is fastened a loop of leather for carrying and holding it while sketching. On one edge of the pad is rigidly attached by clamps a compass in a wooden head and the rulers, giving it the appearance of the sketching-case (Fig. 208), without the rollers. For a clinometer,

the ruler is used as a plumb in connection with a properly graduated line or arc on the opposite side of pad from the compass. As thus arranged, the sketching-pad is used in every respect as has been described for the sketching-case, except that as each sheet of the pad is filled, it is torn off and put in the pocket, and another one filled, etc.

TRAVERSING WITHOUT INSTRUMENTS.-Making the scale. A sheet of paper is fastened on a piece of smooth board or lid of a box, and a straight-edged piece of wood is provided for a ruler.

The sketcher decides on about the scale he wishes to use, then takes a strip of paper of about the length he calculates will represent say 800 to 1,600 paces and folds it three or four times, thus dividing it into 8 or 16 equal parts, each representing 100 paces; these he uses or draws them on the edge of a card for laying off his distances. The smaller distances than 100 paces he can divide by estimation. He can also estimate his offsets in his paces and use the same scale or construct a scale of yards from his scale of paces already made. The representative fraction corresponding to his scale can afterwards be determined when he has access to a scale of equal parts.

Field work. The system to be followed is that which has been already described for traversing with the plane table when orienting by back-sights instead of by the compass. The legs of the plane table have to be dispensed with and the board is laid. as nearly level as possible upon the ground. Stations and prominent objects are located by intersection, the ruler being pivoted on the point on the sketch representing the position of the board on the ground. The ruler is aligned on the different objects whose directions are desired by standing a little distance behind the board and holding the lead pencil vertically several inches in front of the eye and moving sideways until it is in the vertical plane through the object and station point, then noting which way and how much to revolve the ruler, making the alteration, sighting again and altering until aligned; or a stone tied to a string, forming a plumb-line, may be nsed for deter

mining the vertical plane through the object and station point, and aligning the ruler. The surrounding details are sketched in, then the traversing forward to the next station is begun.

When stopping at any time to sketch in details as he arrives opposite them, or on arriving at a station, the sketcher orients his sketch on the back station by placing his ruler along the plotted direction of the course on the sketch, and then, standing behind the board, he determines the vertical plane through the back station and the plotted point of his position, and moves the whole board until the edge of the ruler coincides with the pencil or string defining this plane. Having the board oriented, sightings may be taken to important objects as before. If at a station where a change of direction is to be made, the forward direction is drawn and the traversing continued. Whenever possible, the board should be oriented on the most distant visible objects whose positions have already been fixed on the sketch, rather than by the short back courses. The edge of the ruler is laid on the two plotted points of the distant object and sketcher's position and the board turned until the ruler points to the distant object. The whole operation is nothing more than crude plane table work, and one who can use the plane table will find little difficulty in applying the same principles here.

The true meridian may be approximately laid down on the sketch by determining it at noon from the sun as previously explained.

The sketcher can at any time find his position by resection as with the plane table under the same conditions.

SKETCHING HILL FEATURES.-Contours carry the greatest amount of information with the least amount of drawing in the field, but to sketch them intelligently it is necessary to have a clear idea of the shape of the features and a good mental picture of the appearance they will present in plan.

Supposing stations to have been intersected, and houses, woods, streams, roads, fences, and other details to have been. sketched in by traversing, the operations of sketching the hill

120 Scale of H.E. CI. 10 feet. 3° 1 4° 1 5 1 6° 17° 18° 15° 18

features will be much simplified since the directions of watersheds and water-courses, etc., can often be recognized by reference to the details already drawn, without other measurements.

Suppose the sketch to be made on a scale of R. F. 5000 and hill features to be shown by contours at 10 feet contour intervals. Prepare a table of H.E.'s as follows: 10 feet at 1°-573 feet, 2° 286 feet, 3°191 feet, 4°-143 feet, 5° 115 feet, 6°-95 feet, 7° 82 feet, 8°-72 feet, 9°-64 feet, 10°-57 feet, or draw a scale of the same.

=

To sketch a spur one might, when standing at A on the ground (Fig. 209), whose height above datum has been determined, or assumed, to be 200 feet, observe the slope with his clinometer to be 3° in the direction of a pond. Referring to his table or his scale of horizontal equivalents for 10 feet C. I., he would find the H. E. for 3° to be 191 feet. He paces 191 feet down to B and plots 191 feet to scale on his sketch or lays off the H. E. for 3° from his scale of H. E., fixing the contour point b.